559 research outputs found

    An optical fibre rereadable radiation dosimeter for use at high doses and at elevated temperature

    No full text
    A new type of radiation dosimeter for large radiation doses is described, which is based on silica fibre material. Conventional radioluminescence or thermoluminescence of silica produces emission in the blue region of the spectrum. However, in this new material irradiation, in conjunction with a heat treatment, generates a green emission band. The intensity of the green band can be monitored by either radioluminescence or thermoluminescence using a test dose. The signals are directly related to the total irradiation history of the material. The dosimeter is therefore rereadable. The production mechanism of the green emission centre requires a thermal processing stage, with an activation energy of 0.52 eV. Further, the dosimeter is effective at recording radiation during high-temperature exposure, to at least 400°C, with the subsequent dosimetry being performed below 200°C

    Coupling of effective one-dimensional two-level atoms to squeezed light

    Full text link
    A cavity QED system is analyzed which duplicates the dynamics of a two-level atom in free space interacting exclusively with broadband squeezed light. We consider atoms in a three or four-level Lambda-configuration coupled to a high-finesse optical cavity which is driven by a squeezed light field. Raman transitions are induced between a pair of stable atomic ground states via the squeezed cavity mode and coherent driving fields. An analysis of the reduced master equation for the atomic ground states shows that a three-level atomic system has insufficient parameter flexibility to act as an effective two-level atom interacting exclusively with a squeezed reservoir. However, the inclusion of a fourth atomic level, coupled dispersively to one of the two ground states by an auxiliary laser field, introduces an extra degree of freedom and enables the desired interaction to be realised. As a means of detecting the reduced quadrature decay rate of the effective two-level system, we examine the transmission spectrum of a weak coherent probe field incident upon the cavity

    Thermoluminescence of zircon: a kinetic model

    Get PDF
    The mineral zircon, ZrSiO4, belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such amodel. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time annealing at a given temperature. (iv) Heating of the irradiated sample to simulate TL experiments both after laboratory and natural irradiation. The input parameters of the model, such as the types and concentrations of the TL centres and the energy distributions of the hole and electron traps, were obtained by analysing the experimental data on fading of the TL-emission spectra of samples from different geological locations. Electron paramagnetic resonance (EPR) data were used to establish the nature of the TL centres. Glow curves and 3D TL emission spectra are simulated and compared with the experimental data on time-dependent TL fading. The saturation and annealing behaviour of filled trap concentrations has been considered in the framework of the proposed kinetic model and comparedwith the EPR data associated with the rare-earth ions Tb3+ and Dy3+, which play a crucial role as hole traps and recombination centres. Inaddition, the behaviour of some of the SiOmn− centres has been compared with simulation results.

    Luminescence spectra of germanosilicate optical fibres I - radioluminescence and cathodoluminescence

    No full text
    Data are reported on the luminescence spectra generated by X-ray and electron irradiation of optical fibres, fibre preforms and silica. The impurities and imperfections in the fibre core have a higher luminescence efficiency than those in the substrate material. The core luminescence provides a major fraction of the total light emission, despite the fact that the core is a small fraction of the total fibre volume. A wide variety of overlapping emission bands are reported. The spectra are strongly temperature dependent but the component emission bands can generally be linked to either Ge impurities, giving the 400 nm band, exciton emission near 460 nm or other blue/UV bands linked to E'-type defects. Overall, the study of the fibre luminescence provides a sensitive technique for analysis d changes and repeatability of fibre fabrication

    An aesthetic of the unknown

    Get PDF
    This paper begins to establish an 'aesthetic of the unknown' by drawing together theorists and approaches from mainstream art criticism to provide a starting-point for an aesthetic sympathetic with Jungian perspectives, in an attempt to bridge a gap between contemporary abstract painting, contemporary art theory and Jungian studies. This is a framework for approaching the abstract painting not as an object awaiting interpretation or 'reading', but rather as something that offers a numinous experience (or experience of the unknown), which can be thought about but may remain ultimately unknowable and irreducible. Such experience - involving both the unconscious and conscious mind - would provide glimpsesof forms of meaning not accessible to full rational exposition. This type of uncosciously understood meaning is explored, acknowledging that there is a need to preserve this encounter with the unknown and a need for a contemporary critical, theoretical framework that recognises the importance of this within abstract painting

    Continuous variable entanglement and quantum state teleportation between optical and macroscopic vibrational modes through radiation pressure

    Full text link
    We study an isolated, perfectly reflecting, mirror illuminated by an intense laser pulse. We show that the resulting radiation pressure efficiently entangles a mirror vibrational mode with the two reflected optical sideband modes of the incident carrier beam. The entanglement of the resulting three-mode state is studied in detail and it is shown to be robust against the mirror mode temperature. We then show how this continuous variable entanglement can be profitably used to teleport an unknown quantum state of an optical mode onto the vibrational mode of the mirror.Comment: 18 pages, 10 figure

    Cooling of a single atom in an optical trap inside a resonator

    Get PDF
    We present detailed discussions of cooling and trapping mechanisms for an atom in an optical trap inside an optical cavity, as relevant to recent experiments. The interference pattern of cavity QED and trapping fields in space makes the trapping wells distinguishable from one another. This adds considerable flexibility to creating effective trapping and cooling conditions and to detection possibilities. Friction and diffusion coefficients are calculated in and beyond the low excitation limit and full 3-D simulations of the quasiclassical motion of a Cs atom are performed.Comment: One more figure and one more autho

    Pre-natal and post-natal exposure to respiratory infection and atopic diseases development: a historical cohort study

    Get PDF
    BACKGROUND: According to the hygiene hypothesis, infections in early life protect from allergic diseases. However, in earlier studies surrogate measures of infection rather than clinical infections were associated with decreased frequencies of atopic diseases. Exposure to infection indicating sub-clinical infection rather than clinical infection might protect from atopic diseases. Objective: to investigate whether exposure to acute respiratory infections within pregnancy and the first year of life is associated with atopic conditions at age 5–14 years and to explore when within pregnancy and the first year of life this exposure is most likely to be protective. METHODS: Historical cohort study: Population level data on acute respiratory infections from the routine reporting system of the former German Democratic Republic were linked with individual data from consecutive surveys on atopic diseases in the same region (n = 4672). Statistical analyses included multivariate logistic regression analysis and polynomial distributed lag models. RESULTS: High exposure to acute respiratory infection between pregnancy and age one year was associated with overall reduced odds of asthma, eczema, hay fever, atopic sensitization and total IgE. Exposure in the first 9 months of life showed the most pronounced effect. Adjusted odds ratio's for asthma, hay fever, inhalant sensitization and total IgE were statistical significantly reduced up to around half. CONCLUSION: Exposure to respiratory infection (most likely indicating sub-clinical infection) within pregnancy and the first year of life may be protective in atopic diseases development. The post-natal period thereby seems to be particularly important
    corecore